Generally, semiconductor devices are used in a variety of electronic applications, such as computers, cellular phones, personal computing devices, and many other applications. Home, industrial, and automotive devices that in the past comprised only mechanical components now have electronic parts that require semiconductor devices, for example.
Semiconductor devices are manufactured by depositing many different types of material layers over a semiconductor workpiece or wafer, and patterning the various material layers using lithography. The material layers typically comprise thin films of conductive, semi-conductive and insulating materials that are patterned and etched to form integrated circuits (ICs). There may be a plurality of transistors, memory devices, switches, conductive lines, diodes, capacitors, logic circuits, and other electronic components formed on a single die or chip, for example.
There is a trend in the semiconductor industry towards reducing the size of features, e.g., the circuits, elements, conductive lines, and vias of semiconductor devices, in order to increase performance of the semiconductor devices, for example. The minimum feature size of semiconductor devices has steadily decreased over time. However, as features of semiconductor devices become smaller, it becomes more difficult to pattern the various material layers because of diffraction and other effects that occur during a lithography process. For example, key metrics such as resolution and depth of focus of the imaging systems may suffer when patterning features at small dimensions.
Innovative process solutions have been developed that overcome some of these limitations. However, many such process solutions also interact with subsequent steps and may degrade other equally important factors.
For example, another goal of the semiconductor industry is to continue increasing the speed of individual devices. Enhancing mobility of carriers in the semiconductor device is one way of improving device speed. One technique to improve carrier mobility is to strain (i.e., distort) the semiconductor crystal lattice near the charge-carrier channel region. Transistors built on strained silicon, for example, have greater charge-carrier mobility than those fabricated using conventional substrates.
One technique to strain silicon is to introduce stressor materials. Stressor materials exert strain on the channel of a device by various means. Examples of such methods include lattice mismatch, thermal expansion mismatch during thermal anneal, and/or intrinsic film stress. A typical transistor fabricated today comprises all these elements. The use of SiGe source/drain regions is an example of using lattice mismatch for producing strain. Examples of thermal mismatch and film stress include stress memorization layers and contact etch stop layers.
One challenge with strain techniques arises from their layout effects. Channel strain not only depends on the stressor material, but also on the location and placement of these materials. Hence, any modifications made for example, in the printing of these features during the lithography steps can seriously impact transistor performance and hence product performance.
Solving such interactions requires cross-functional development with information and knowledge sharing between different organizations. What are needed in the art are methods of leveraging lithography to enhance design and manufacturing processes.